A new record has been set in Australia’s gold miners’ own journey to the centre of the earth, with Northern Star Resources claiming to have drilled the deepest hole in national exploration history at its Jundee operations near Wiluna.

Targeting underneath Northern Star’s new Zodiac discovery, contractors DDH1 Drilling started the diamond drill hole from surface on December 15 last year and wrapped it up on February 28 at a length of 3217m, finishing at a vertical depth of 2625.1m.

That made it more than 200m longer than a hole snaking underneath Kalgoorlie’s Super Pit in 2015, which reportedly stopped at 3011.5m.

Originally slated to wrap up at 3100m, Northern Star Resources chief executive Stuart Tonkin said the hole was pushed to the drill’s technical limit after it found “something interesting” just before its planned end point.

Mr Tonkin said mining companies had more incentive to undertake higher-risk exploration activities because it was getting technically harder to make new discoveries, with most of the low-hanging fruit in WA’s gold inventory already picked off.

“These mines are getting harder to extend and explore and I think all companies you’re starting to see them step outside of convention and take higher risks because discoveries are more technically challenging, they’re undercover, they’re more expensive and they’re higher risk,” he said.

“You’re starting to see companies having to do that out of necessity because they’ve got declining reserves.”

The hole drilled was targeting “reflectors” identified in a seismic survey beneath the Zodiac discovery, about 800m east of the Jundee mine. While this hole extended far beyond that, Mr Tonkin said it helped Northern Star understand the source and continuity of the Jundee mineralisation.

Jundee, 45km north-east of Wiluna in the northern Goldfields, has a reserve of about 1.4 million ounces, with Northern Star planning to ramp up production in the coming years.

The company said it had “mine life visibility” of about 10 years at Jundee.

It is not the only company drilling deep on exploration holes typically costing well over $1 million.

DDH1 is also working on a 2950m deep hole at St Barbara’s Gwalia gold mine near Leonora, while junior explorer Artemis Resources is also planning to launch a campaign, drilling to 3300m in the Pilbara.

Northern Star shares were off 1c, or 0.2 per cent, to $6.58 yesterday.